1. Field of the Invention
The present invention relates to a dithering method and a dithering device. Particularly in the case of Plasma Display Panels (PDPs), but also in the case of other devices, such as, Plasma Addressed Liquid Crystals (PALCs), one of the problems which occurs is that because of physical limitations, the number of bits available for a pixel value of a particular color cannot be displayed in sufficient depth. Due to lack of time, six to eight bits per image cycle are, for instance, possible in the case of PDPs, while the (color) information is available in, for instance, ten to twelve bits.
2. Description of the Related Art
Dithering algorithms are known, such as that of Floyd-Steinberg, error diffusion etc., for compensating truncation errors.
It is known, for instance, from U.S. Pat. No. 5,404,176, to add a bit value of a color component (R, G, B) and a random number, and thus compensate for a truncation error.
It is an object of the present invention to provide a good dithering method and dithering device, wherein the calculations are not very complex and the required hardware and/or software can remain limited.
The present invention provides a dithering method for assigning a digital value of N bits to a color component of a pixel, wherein the image signal comprises a pixel value of M bits, wherein M is greater than N(M greater than N), wherein a (pseudo-)random number of (Mxe2x88x92N) bits is added to an original pixel value of M bits, the result of the addition then being truncated at N bits, and wherein the two or more random values which are added to two or more adjacent (color) pixel values are mutually correlated.
According to the present invention the (software) computation for dithering noise can be combined with the gamma correction, which is especially important for PDPs. If combined with gamma correction, the algorithm, according to the present invention, adds 27 MHz instead of 119 MHz for the Floyd-Steinberg algorithm of computing capacity for a processor of 1000 MHz, e.g., a load of less than 3% instead of about 12% relative to the capacity of the processor.
Two of the random numbers are preferably each other""s inverse, and more preferably, four random numbers originate from a common random generator wherein pairs of the numbers are each other""s inverse. So-called xe2x80x98blue noisexe2x80x99 is hereby obtained in a higher frequency range than if the values were uncorrelated, which is advantageous for the Human Visual System (HVS).
In order to keep the total luminance value of successive pixels as constant as possible, the respective different mutually correlated random numbers are added as far as possible to the respective pixel values for red (R), green (G) and blue (B) of successive pixels.
The present invention further provides a dithering device which particularly makes use of a plasma display panel.